I think this would make a cool study. You could probably do it through myspace, or hotornot, or some similar site. Correlate how many friends someone has with how their looks are rated by the community.

But without data, as an un-beautiful introvert, I think your boss's theory makes sense. Extroverts enjoy interacting with lots of people they don't know well. To do that, it helps if you look good, so presumably they strive to look good. Clothes, makeup, hairstyle, etc.

Introverts enjoy being alone, or interacting with a few people they already know really well. In those situations, how you look doesn't matter as much, so there's less incentive to prettify yourself.

But it's not just that introverts don't waste time on beauty and extroverts use it as an essential skill. I'd argue that someone beautiful will get better reactions from strangers, and will therefore be more comfortable around them. Growing up beautiful might _make_ you extroverted, while being ugly might make you introverted. c.f. Quasimodo.

Sure there are some inherently beautiful introverts (I've known a few) and maybe some ugly extroverts that neglect personal appearance and get by on charm, personality, or wealth, but the rule could still work on a general basis.